The invention generally relates to devices and device fabrication and, in particular, to devices having a layer for facilitating passivation of surface states and a process for fabricating such devices.
In device fabrication, insulating, semiconducting, and conducting layers are produced and patterned on a substrate to form device structures, such as transistors, capacitors, or resistors. These device structures are then interconnected to achieve a desired electrical function. The production and patterning of the various device layers are achieved using conventional fabrication techniques such as, for example, oxidation, implantation, deposition, epitaxial growth of silicon, lithography and etching. Such techniques are described in S. M. Sze, xe2x80x9cVLSI Technologyxe2x80x9d, 2nd ed., New York, McGraw-Hill, 1988, which is herein incorporated by reference for all purposes.
Conventional fabrication techniques induce various forms of defect or damage to the layers within the device. For example, damage to chemical bonds at the semiconductor interfaces creates dangling bonds known as surface or interface states. Surface states promote recombination of electron-hole pairs. Recombination is a phenomenon whereby electron-hole pairs are annihilated or destroyed. Recombination, particularly if it occurs at critical device interfaces such as isolation perimeters and gate oxides, results in leakage current. Leakage current alters the gate threshold voltage, data retention, and standby power consumption of devices. Thus, the presence of interface states adversely affects device functions.
Surface states are repaired by providing hydrogen atoms to passivate the dangling bonds. Conventionally, relatively high temperature anneals, typically about 400 to 600xc2x0 C., in hydrogen-containing ambients have been employed to supply hydrogen to passivate the dangling bonds. The passivation anneal is usually performed late in the device fabrication processing sequence, such as after the formation of the various layers, including the metallization or interconnection layer. This reduces the number of passivation anneals required to repair the dangling bonds created during previous fabrication processes. Reduction in the number of passivation anneals reduces process costs.
However, current interconnection schemes and device structures tend to inhibit the ability of the hydrogen atoms from reaching the recombination sites to passivate the dangling bonds. As such, the effectiveness and efficiency of the passivation anneal is reduced. For instance, silicon nitride deposited by low pressure chemical vapor deposition (LPCVD), which serves as a mobile ion and transition metal diffusion barrier, blocks the diffusion of hydrogen. This LPCVD silicon nitride film prevents hydrogen from penetrating to the layers below to passivate the surface states existing in those layers. In tungsten stud structures, the tungsten quenches the hydrogen, producing a similar effect as the silicon nitride layer. The efficiency of passivation anneals is further reduced since nitrogen gas is often used to dilute the hydrogen (forming gas) in order to decrease the inherent danger associated with the explosive nature of hydrogen.
From the above discussion, it is apparent that there is a need to effectively passivate the surface states caused by device fabrication techniques.
The invention is generally related to device fabrication. As known in the art, conventional device fabrication techniques damage chemical bonds, creating surface states at semiconductor interfaces. These surface states are repaired or passivated by supplying hydrogen atoms during a hydrogen anneal. However, current device structures tend to block hydrogen from reaching and passivating the surface states.
To overcome the passivation problem that exists with current device structures, a process for fabricating a device is disclosed. The process includes the step of fabricating a device structure which facilitates the passivation of surface states. The device structure comprises an oxynitride layer. In one embodiment, the oxynitride layer is formed by plasma-enhanced chemical vapor deposition (PECVD).